China last week announced it started operations of the stations on three islands to offer weather forecasts to fishermen in the South China Sea region and neighbouring countries as well as passing ships.

Vietnamese Foreign Ministry spokeswoman Le Thi Thu Hang told reporters at a regular briefing Thursday that Vietnam has legal basis and historical evidence to assert its sovereignty over the Spratlys and Paracels and asked China to stop the action.

“The fact that China started use of meteorological observation stations on the illegally built structures in the Spratlys has seriously violated Vietnam’s sovereignty over the islands,” she said.

“Vietnam persistently opposes this act and asks China to immediately stop the above-said actions,” she said.

Hang said China should abide by the principles reached between the two countries guiding the settlement of the maritime issues and the Declaration of the Code of Conduct in the South China Sea “without complicating the situation, affecting peace, security and stability” in the South China Sea.

Vietnam and China along with five others claim all or parts of the Spratlys. Tensions have flared after China turned seven disputed reefs into islands, which it later equipped with missile defence systems.

Vietnam has become the most vocal against China’s growing assertiveness in the South China Sea, which has triggered concerns and protests in the region as well as the United States.